Adjusting mechanism for load compensating brake apparatus



D. M. HART CHANISM FOR LOAD COMPENSATING BRAKE APPARATUS Filed July 26.1949 ADJUSTING ME Jply 29, 1952 INVENTOR. DUANE M. HART ATTORNEYPatented July 29, 1952 ADJUSTING MECHANISM FOR LOAD COM- PENSATING BRAKEAPPARATUS Duane M. Hart, Pittsburgh, Pa., assignor to Westinghouse AirBrake Company, a corporation of Pennsylvania 4 Application July26, 1949,Serial No. 106,823

11 Claims. 1

This invention relates to fluid pressure brakes and more particularly tothe compensating type for varying the degree of brake application on acar in substantial proportion to the load carried by the car.

In the copending application, Serial No. 736,010 of Earle S. Cook, etal., filed MarchZO, 1947, now Patent No. 2,482,246 issued September 20,1949 and assigned to the assignee of this application, there isdisclosed a load compensating fluid pressure brake apparatus includingmeasuring means arranged to cooperate with an-unsprung part of-a car foradjusting said apparatus to limit the degree of brake application on thecar in accordance with the deflection of the car springs and hence insubstantial proportion to the load on the car. When the brake apparatusis initially installed on the car the measuring means is properlyadjustedfor a fully loaded car to accomplish this result. After a car isplaced in service however, there is a tendency for the load carryingsprings to gradually shorten, for

any chosen load carried thereby, to a so-called permanent set condition,resulting in a gradually decreasing deflection of the car springs forany change in load on the car, so that the measuring means, as initiallyadjusted for the new car with new springs, will not accurately adjustthe brake apparatus to the degree of load on the car after the car hasbeen in use.

The principa1 object of the inventionis therefore the provision of meansfor automatically compensating for a change in deflection characteristicof car springs, such as above mentioned,

so as to provide substantially the same adjust- .in Fig.1; Fig. 3 is asectional view of said measuring arm taken on the line 3-3 in Fig. 2;Fig. 4 is a sectional view of said measuring arm taken on'the line 4-4in Fig.2; Fig. 5 is a sectional view of said measuring arm taken on theline 5-=5 inF-ig. 2; and Fig. 6 is a view of a portion of the measuringarm looking in the direction of arrow A in Fig. 2.

' Description As shown in the drawing, the reference numeral ldesignates an-adiusting means or meas- A uring arm, embodying theinvention, for a load compensating brake apparatus, such as disclosed inthe above mentioned copending application, said arm being pivotally,connectedjto one end of an operating lever 2 by a bolt 3 (Fig. 3).. Thelever v2 suitably fulcrumed at its other end on a pin 4 carried by a carcenter sill 5 or some other sprung part of the car which is supported bythe usual truck springs -6. Lever 2 is connected "in!- termediate itends to a load compensating valve device 1 by means'of a link 8 andacrankarm 9'. The load compensating valve device I is suitably mountedupon center sill 5 in the usual manner by any suitable means (not shown)The load compensating valve device 1 maybe the sameas that fullydisclosed and describedin the above mentioned 'copendin application, andadapted to operate during initial charging ofa brakepipe H] fromatmospheric pressure to a certainchosen higher pressure to move themeasuring arm I into engagement with an unsprungpart of the. car truck,such as. a measuring element II which is welded or otherwise suitablyfastened to an unsprung truck frame l2, for adjusting .said. valve,device in accordance with the deflection: of springs 6, and hence inaccordance with the load on the car, for limiting the degree of a brakeapplication correspondingly.

In the drawing, the load compensating valve device I is merely shown inoutline since it forms no part of the present invention and referencemay be had to the above mentioned .copending application for details ofconstruction andoperae tion thereof. if Considering the parts of themeasuring arm 1 in detail, as shown in Fig. -2',..said arm comprises abody l3 having a chamber 14 which is prefer.- ably rectangular incross-section. :Slidably mounted in chamber [4 is a plunger l5 ,-theout.- side contour of whichconforms to the .rectangular shape of chamber[4. Plunger 15 is proe vided with a stem I6 normally extendingthrough around bore I! in body 13 acertain chosendise tance, the end of said stembeing spacedfrom an adjustable stop in the form of a cap screw sl8having screw-threaded engagement With a bracket l9 which may be weldedor otherwise fastened tocenter sill 5. A look nut Zllisprmvided on capscrew I8 for engagementwith bracket H) to lock said cap screw in any oneof a plurality of positions relative to said bracket 19 to adjust thedistance betweenth'e adjacent end of stem I6 and a head 2| of said capscrew.

Plunger I5 is also provided withtwo cavities or spring chambers 22 and2-3, cavity 122 being coextensive with a cavity 24 formed in, body I 3,

said cavity 24 being closed by a cover to ex'- clude dirt and water.Plunger I5 is further provided with a square bore26 in which isslidablydisposed a vertically arran ed square :rack

from any point on one tooth to the corresponding 7.

point on the adjacent tooth is equal to the distance that stem I6normally projects beyond the top' of body I3. The purpose of makingthesedistances equal will be explained hereinafter in greater detail. Thelower end of rack 21 is re-' duced in cross-sectional area and providedwith screw-threads for screw-threaded engagement with an upper threadedportion 29 of a measuring leg 30. Measuring leg 39 comprises in additionto portion 29, a contact foot or hook 3| adjustably but rigidlysecuredto threaded portion 29 by means .of' bolts .32.. By reason of aslot in threaded portion 29 through which the bolts 32 extend J andcomplementary serrated faces of threaded portion 295and foot 3|, whichfaces are indica'ted'at 33,- the overall length of measuring leg; 30.may be varied as desired by adjusting the position'of foot 3| relativeto portion 29 with bolts 32 loosened and then tightening said bolts.Foot 3| is! provided on itsupper side with a surface 34 for'contact withthe lowermost part of unsprung measuring element I I in amannerexplained more fullyhereinaften V g I @Above the serrated face ofthreaded portion 29 said portion is preferably square in cross-section(Fig.4), and passes through a square bore 35 in a cap 36 which closesthelower end of chamber I4, said cap being fastened tobody I3 by anysuitable means (not shown) Thethreaded portion 29 of leg 30 isprovidedwith a slot 3'! located a distancebelow the bottom surface of cap 35equal to the length of the toothed portion of rack 21.

The upper end of the square bore 26 is closed by awall 38 constituting apart of plunger I5. A spring,3r9 supported by. rack 21 bears againstwall 38 for urging said rack in a direction away from wall38.1 Twoidentical but oppositely arranged pawls 49 and are provided, each forengaging one of the two rows of teeth. 28 on rack 21. Pawl 4D is pivotedineavityM on a pin 42,,carried by body I3. Two springs 43 and. areopposingly connected to pawl 40 at the same sideof its pivot, saidsprings having the same change in pressure per unit deflectioncharacteristics, said characteristics being greater than thecorresponding characteristic of spring 39. Springs 43 and 4 4 areanchored .on pins, 45and 46 respectively, carried by body I3.. BawlAlispivot'ed in cavity 23 on a pin 4! carried by plunger 'I 5. in Twosprings, 43 and 49 are opposingly connected to, pawl M at the same sideof its pivot,,said springs having the same change inpressure per, unitdeflection characteristics as springs 43, 44. Springs Mandflfigareanchored on pins 50 'andi I, respectively, carried byvplunger Disposedin, chamber I 4 between capte and plunger I is aspring izgfor urgingsaid plunger inthe direction of a stop 5; constitutingthe top w llq bedfl- .7 A. v r

' Operation "Atthe time the measuring arm I is assembled, the pawls. 40and 4| are positioned to engage respectively, the top most teeth of thetwo rows of teeth 28 inwhich position they are shown in Fig. 2 of thedrawing. At the same time contact foot 3i is fastened to the lower endof the serrated face 'of threaded portion 29 by means of bolts 32 asalso shown in Fig. 2. With measuring arm I thus assembled, it, togetherwith cap screw or adjustable stop I8, bracket I9 and lock nut 20 areinstalled on a railway car in the position in which they are shown inFig. 1 of the drawing. When measuring arm I, adjustable stop I8, bracketI8, and lock nut 20 are thus installed on a car, said adjustable stop isadjusted with respect to said bracket until the distance between theundersurface of said stop and the top surface of stem I6 is equal to thedistance between surface 34 of contact foot 3| and the lowermostundersurface 9f measuringelement II when the car is fully loaded.Withadjustable stop I8 in this adjusted position, lock nut 20 is lockedagainst the under surface of bracket I9 to lock said stop in itsadjusted position. The load compensating valve device I and measuringarm I are now conditioned to effecta load measuringoperation.

With no fluid under pressure present in brake pipe l0, and with the carfully loaded and having new springs, the various parts of the brakeapparatus will occupy the position in which they are shown inrFig. 1 ofthe drawing. To condition the equipment for operation, fluid underpressure is supplied to brake pipe If) in the usual manner. When thepressure of fluid in brake pipe Ill is increased to the certain chosenpressure, during initial charging of the brake pipe, crank arm 9 will berockedin a counter-clockwise direction by fluid under pressure suppliedto the load compensating valve device I and pull link 8 and operatinglever 2 in an upward direction, said lever rocking about its pivot pin4. This movement of operating lever 2 will in turn lift measuring arm Iupward, said arm rocking, due to its own'weight, relative to said leverabout its pivotal connection'therewith, and thereby remaining ina'vertical position. Measuring arm I will be lifted vertically to bringthe top surface of stem I6 into engagement with the bottom surface ofhead El and surface 34 of leg 30 into engagement with the lowermost partof unsprung measuring element II, the two engagements occurringsimultaneously with the car fully loaded since the distances between thetop of stem I6 and head 2I, and top surface 34 and measuring element II,were adjusted to be equal when the equipment was installed on the car aspreviously explained. Upon surface 34 engaging the lowermost part ofunsprung measuring element I I further upward movement of measuring armI will be arrested and the load compensating valve device I willbe'conditioned in a manner fully described in the above mentionedcopending application to provide for the proper braking force on thefully loaded car. 7 r T Now let it be assumed that after the car hasbeen in service the truck springs 6 have shortened permitting the carcenter sill 5 to assume a vertical position closer to truck frame I2than permitted when said spring were new, for any chosen degree of loadon the car. As a result of the shortening of springs 6, measuring arm 39also'will be in a lower position than when springs 6 were new, with agreater distance between surface 34 of contact foot 30 and the lowermostpart of unsprung measuring element II, but the distance between the topof stem I6 and the bottom of head 2| of adjustable stop I8 is the sameas when springs 6 were new since said stem and stop are both carried bythe sprung center sill 5.

With springs 6 thus shortened, upon initially charging the brake pipeI!) on a fully loaded car, the crank 9 will be rocked, as beforedescribed, in a counter-clockwise direction for lifting measuring arm Iupward. As measuring arml i thus lifted upward, stem It will engage thehead 2| sprung measuring element H is less than when the car is fullyloaded, but the distance between the top of stem I6 and the bottom ofadjustable stop 2| is the sameas when the car is fully loaded. Thereforesurface 34 will engage the lowermost part of unsprung measuringelement'll without the top of stem is engaging the bottom of head 2| ofadjustable stop I8. Upon surface 34 thus engaging element furthercounterclockwise rocking of crank arm 3 and upward movement of measuringarm is prevented whereupon the load compensating valve device I will beconditioned to provide the proper braking force fora partly loaded carin a manner fully explained in the hereinbefore mentioned copendingapplication. The engagement of surface 34 of contact foot 3| withelement II when the car is less than fully loaded, thus preventsengagement between stem Hi and adjustable stop |3 and consequentialratcheting of measuring leg 30 with respect to body I3 as has beenexplained in connection with a load measuring operation on a fullyloaded car. It isevident therefore, that load measuring operationsoccurring, whilethe car is less than fully loaded, are without efiect onthe distance between surface 33 of contact foot 3! and the lowermostpart of upsprung measuring element l, which distance is effected byshortening of springs 6.

In the manner above described, the position of rack 21 within the body.l3 may continue to be changed as thesprings 6 become shorter until pawlsS6 and 4| have ratcheted over the total number of teeth on rack 21 atwhich time slot 3? will be flush with the bottom surface of cap 33 thisbeing an indication to an observer that the measuring arm is no longereffective to compensate for shortening of the springs 6 and requiresresetting.

In order to reset the arm I, the arm 36 will be manually moved into body|3 to permit the adjacent ends of. pawls 40, 4| to ratchet over thelowest teeth 28, unless said pawls have already done so, whereupon thepawls 40 and M will be rocked by springs 33 and 48, respectively, fromthe position in which they are shown in Fig. 2 of the drawing to aposition in which the force of each of the two springs acting on each ofsaid pawls will be equal and in which latter position the respectiveright and left hand ends of said pawls will be disposed in engagementwith a surface 54 formed on the lower end of rack 2! beneath the teeth28. With pawls 4i] and 4| thus disengaged from the teeth 28 and the endsthereof engaging surface 56, measuring leg 39 may be reset.

To reset measuring leg 36, said leg may be grasped with the handexteriorly of body |3, and pulled in a downward direction. Downwardmovement of leg 36, as just described, causes pawls'flil and 4| to berocked in clockwise and counter-clockwise directions respectivelyagainst the tension of springs 44 and 49 respectively, until the righthand end of pawl 40, and the left hand end of pawl 4| are moved out ofengagement with surface 53 and to a position in which said ends willpermit rack 2! to be moved downward until a surface 55 on said rack isbelow said ends, whereupon the tension of springs 44, 45, 48 and .43will equalize and throw the pointed ends of pawls 40 and 4| back intothe path of movement of the rack teeth.

To continue the resetting operation, measuring leg 30 now may be pushedupward by hand against the force of spring 39 until pawls 4|] and 4|engage the respective uppermost teeth of the left and right hand rows ofteeth 28 on rack '21. Pawls 40 and 4 will now occupy the position inwhich they are shown in Fig. 2 of the drawing.

After the measuring arm 39 has been reset as just described, said armwill occupy the same position relative to body l3 as it occupied priorto the shortening of springs 6. It should be noted however, if thedevice is being reset to compensate for further deformation of the carsprings 5 that the distance between surface 34 of contact foot 3| andthe lowermost part of measuring element II- is not the same as it wasprior to the initial shortening of springs 6, since the shortening ofsprings 6 permitted center sill 5 and measuring arm 1 carried thereby toassume a vertical position closer to truck frame |2 than permitted whensaid springs were new. Therefore, with the car fully loaded and withmeasuring leg 30 reset to occupy the same position relative to body l3as it occupied prior to the shortening of springs 6, surface 34 ofcontact foot 3| will be disposed in a position-further below measuringelement |i than the position in which it was disposed when springs 6were new. As is explained in the hereinbefore copending application, theload compensating valve device 1 provides a braking force on the car inaccordance with the distance between surface 34 of contact foot 3| andthe lowermost part of unsprung measuring element For this reason it istherefore necessary to readjust contact foot 3| with respect to upperthreaded portion 29 until the distance between surface 34 and thelowermost part of measuring element is the same for any load as it wasprior to the shortening of springs 6.

To eifect such readjustment, the bolts 32 are loosened and contact foot3| moved upward with respect to upper threaded portion 29 and measuringelement until the desired distance between surf-ace 34 of said foot andthe lowermost part of said measuring element is obtained, at which timesaid bolts are tightened to rigidly secure said foot to said threadedportion. With contact foot 3| thus readjusted with respect to upperthreaded portion 29, measuring-arm is conditioned to compensate, uponsubsequent load measuring operations occurring on a fully loaded car,for further shortening of springs 6 in the same manner as abovedescribed.

The measuring arm I may be so designed as to compensate for either fullor only partial change in the deflection characteristic of the springs6. If designed to compensate for only partial change in the deflectioncharacteristic then it will be necessary to reset the leg 33 relative tobody l5 back to its original position as above described and also bymeans of bolts 32 readjust the foot 3| relative to threaded portion 29and measuring element to provide the same distance between surface 34and measuring element H as existed at the beginning when the springs 6were new, whereupon the measuring arm will operate the same as abovedescribed to compensate for further change in deflection of springs 6.

If however, the design of the measuring arm is such as to compensate forfull permissible change in deflection characteristic of the car springs6,

59f." them-upon said springs {being .replaced .by new springs:it will:.be necessary toreset thearmand readjust the foot .34 "to the newsprings in .a manner which will :be evident from the. above remarks.

um ry lt w llsnow be seen tha IhaveproYided alood measuring apparatusfor-use ith load com ensat neifl idn essur b e eq ipment on rai wa aremb dyin me n v r a tom cally omp nsat n r -.cha ,ge. in he defl ion-chractersti o t uck s s s as t ipr vide subs a daily t s m adjustm t :o hc m n a ing brak appa a zu fo n loa on th ca h ou hout the i coi sa spngs as r v de w en th sprin ,a' ew- :Hayins d s bed. m invention what .Ic aim was new and desire ,to secure by Letters atent 1.

--A.mea u oe mec ani m fo t-a l ad compons inezbra e equ m n or t u-vehle h in a unso u s a ao carr n s run art. nd sprin m ans restin o saidun p un pa a uppor ing s id sprung v s id me suri mechanism ,comprisingafixed measuring stop on said unsprung part, :a measuring arm rockablymounted on said sprung part, and power means for.,actuating1said arminto engagement with said stop, said ear-m comprising a casing.operative y connected to said power means, anengagine a m r en a ementwith sa d stop, and v pa an ratchet mechanism a t m t ca opera ve bysaid :DOWer: means tor-adjust said arm relative to said casing 'upon ar'eduction in the height of soidcs rio mean in id n to a han i dflection ofzsaid spring means :for any chosen load n-sai so nerar z hmeasuring mechanism for .a load compensating-brake equipment-foravvehicle having a sp ains p t o ons un art and sprin s restinson, saidun spltun g part and supporting said sprung part, said mechanismcomprising a fixed op on th sprun ha t an -a fi e op o t unsprung part,a measuring-arm carried by said sprung part and comprising-a casing aleg: for movementpy said casing into engagement with a d: sto onssa donso oe pa t a p n a c mechan m o n c ng: said leg to said casing; I anda member associated with said casing disposed .irom saidstop on said-sprung parta distancesequal -to.. the distance th-atsaid leg isdisposed irom said stop onsaidunsprung part at johetime the-.vehicle;-is fully loaded and said springs are, new: and operative, .uponsettling, of saidsprih s, into engagement with the stop on said sprnngpart prior to engagement-of said le withsaid stop-on saidunsprung partto operate said mechanism to ratchet said leg relative tosaid casingsacertain chosen distance, and means for moving said casing, said leg andsaid member relative to saidstops.

.3. A measuring mechanism for ,a load compensating brake equipment foravehicle having a sprung part, an unsprung part and spring means restingon said unsprung part and supporting said sprung; part, saidmechanisrnuccmprisinga f xed stop on said sprun ,partand a'rflxe o onsainnspnungt'nart, a measurin a m-c prisinetw morab1 .:mcmber one o whi hosed :th same distance from one of said stops as the other is disposedfrom the other of said stops only at the time the vehicle is fullyloaded and said spring means are new, means operative to move said oneand other members into engagement with, re-

spectiv ly, a d o e and othe atoll @93 M Operative upon enea emento on ohers w th t sto p o 11 neoe m other ofs id members withit -stont v o hermember a chos n distanc @in the direct on oiitsresnectivestop. V 7 v 4.A me uri mechanism fo load v151. -v nensat n .Jorak e uipment. or avegclha n asprungpa t, an un runs andso nem a is restin on saiduosp unspar-tand-sup ort n .d prun -par so dmechahism comprisin 1 3 st p on eac noft'aid rronsand .o sPrtnehettsi arme sur n arm; h in anon na ivcPosition-ad an inoperat ve pos ion a com i he a first member which i he; nope ativhosition ofsoi arm i isposed om-said stop on sa uhsp .e' parts di tancethat.veriesac ord ne: qth ad ont e voh l nan th com es ed hei ht o aidsprin means, a second memb r t onnocted :to said first memb r an dis o en th inoperative. posi on of said arm/ir m ai toio onsaidso un member adistance equal to the distance saidtfirjst member; s di posed from. s idstop onssaid .un-

aid

measurin m. chaois niton a .loadlcome n-chsotine a quspm t rto g ;yeh olhe ins tes in o e d; e spr n -toa ts saids c an sm oo stoco 1eech; -spow mean @9 3 9. 9 soi $1 0 m vab ezmcmh so o said teosoruo 5??4' 2toothed segment, a pan/tan ratchetrn ch A etIectivenpon each 1 operationthereof; to ratchet twe n W o L bl oemte o o A messa e ileef -is ooly-di osed n-I h tin forme o po io 1 s t id m t sense ieth o ho aoe ofsaid s r operable by an external force for ratchetlng 7. A measuringmechanism for a load compensating brake equipment for a vehicle havingan unsprung part, a load carrying'sprung part, and spring means restingon said unsprung part and supporting said sprung part, a lever rockablymounted at one end on said sprung part, a measuring arm rockably mountedat one end on the opposite end of said lever and comprising a casing,'amovable engaging leg for engaging an undersurface of said unsprung part,a ratcheting means for locking said engaging leg against movemeritrelative to said measuring arm, and means operable in one direction toratchet said leg relative to said casing, spring means operable to movesaid ratcheting means in an opposite direction, power means foractuating said lever, and means for effectin operation of saidratcheting means upon said power means rocking said lever throughgreater than a chosen angle, said greater angle being a function of achange in the pick up characteristic of said first mentioned springmeans.

8. A measuring mechanism for a load compensating brake equipment for avehicle having an unsprung part, a load carrying sprung part, a stop oneach of said parts and spring means resting on said unsprung part andsupporting said sprung part, said mechanism comprising a lever rockablymounted at one end on said sprung part, power means for rocking saidlever, a measuring arm rockably mounted at one 'end on the opposite endof said lever and comprising an engaging leg having a hook for engagingthe undersurface of said stop on said unsprung part, a ratcheting meansconnected to saidleg, and a plunger mechanism operative by said powermeans to engage said stop on said sprung part simultaneously with theengagement of said stop on said unsprung part by said engaging leg andoperative by said power means upon engagement with said stop on saidsprung part prior to the engagement of said stop on said unsprung partby said engaging leg to operate said ratcheting means to ratchet saidleg relative to said plunger.

- 9. A measuring mechanism for a load compensating brake equipment for arailway freight car having an'unsprung truck member, a plurality oftruck springs resting on said truck member, a sprung load carryingmember supported by said springs, a first stop associated with saidtruck member and a second stop associated with said sprung member, alever rockably mounted at one end on said sprung member, power meansmounted on said sprung member and operatively connected to said leverfor effecting rocking thereof, and a measuring arm rockably mounted atone end on the opposite end of said lever, saidmeasuring arm comprisingtwo movable elements so disposed that upon the car being fully loaded,one of said element will be disposed substantially the same distancefrom said first stop that the other element is disposed from said secondstop, and means operative by said power means in case of an increase inthe distance between said one element and its respective stop to adjustsaid one element relative to said last mentioned stop to reduce suchdistance.

10. A measuring mechanism for a load compensating brake equipment for avehicle havin an unsprung part, a' load carrying sprung part,

spring means resting on said unsprung part and supporting said sprungpart, and a stop member on each of said parts, 'said mechanismcomprising a lever rockably mounted at one end on said sprung part,power means for rocking said lever, and a measuring arm rockably mountedat one end on the opposite end of said lever and comprising a hollowcasing having a stop at each end, a plunger slidably mounted in saidcasing between said stops, an engaging legmounted to slide in saidplunger parallel to the direction of its movement and extendingexteriorly'from said casing and having at its outer end a hook forengagement with said unsprung part and having within said casing ratchetteeth, a first pawl pivotally carried by said plunger, spring meansanchored on said plunger for biasing said first pawl into engagementwith certain of said teeth, a second pawl pivotally carried by saidcasing, second spring means anchored on said body and biasing saidsecond pawl into engagement with other of said teeth, means operative tomove said plunger in one direction to cause said first pawl to ratchetover one of said teeth, and structure operative subsequent to theoperation of the last named means to move said plunger in the oppositedirection to cause said second pawl to ratchet over one of said teeth. 1

11; In combination, two stops, a casing disposed between said stops,means for moving said casing in the direction ofeither one of saidstops, a plunger slidably mounted in said casing, a stem formed integralwith said plunger and extending a'chosen' distance outside of saidcasing to engage one of said stops upon said casing being moved in thedirection thereof, an engaging leg slidably mounted in said plungeraxially thereof and extending to the exterior of said casing in adirection opposite to the direction of said stem, said leg having at itsouter end a hook for engaging the other of said stops upon movement'ofsaid casing in said one direction and having at the opposite end ratchetteeth the pitch of which is equal to said chosen distance, two pawls onecarried by said casing for moving said leg with said casing and relativeto'said plunger 'for ratcheting the other pawl one tooth upon movementof said casing in one direction relative tosaid plunger, and said otherpawl carried by said plunger for holding said leg against movementrelative to said plunger upon movement of said casing-in the oppositedirection relative to Said plunger for ratcheting the one pawl onetooth, first spring means carried by said casing and operative to biassaid one pawl into engagement with certain of said teeth, and secondspring means carried by said plunger and operative to bias said otherpawl into engagement with other of said teeth. r DUANE M. HART.

REFERENCES CITED i V The following references are of record in the fileof this patent:

UNITED STATES PATENTS Cook Sept. 17, 1946

